1. Field of the Invention
The present invention relates to a driving device, a driving circuit, an LED head, and an image forming apparatus.
2. Description of Related Art
Japanese Patent Application Publication No. H10-332494 is known that discloses a technology relating to a driving device for driving a driven device such as an LED array and the like.
Specifically, Japanese Patent Application Publication No. H10-332494 discloses a driving device that has driving circuits having temperature compensation circuits and decoupling capacitors respectively connected to the driving circuits, so that the driving device reduces a noise voltage. More specifically, the temperature compensation circuit detects a temperature by using base-emitter voltages of two bipolar transistors whose size are different from each other. A reference voltage is calculated by making use of a fact that a difference between the base-emitter voltages of the two bipolar transistors is proportional to a thermal voltage VT. The driving device drives the driven device by supplying the calculated reference voltage to the driven device. The thermal voltage VT is such extremely low signal level, approximately 26 mV at room temperature. Accordingly, the driving device gets rid of the effect caused by the minute noise voltage occurring within the driving circuit by arranging the decoupling capacitor connected to each of the driving circuits, thus reducing the influence caused by the noise voltage.
In a case where the driving circuit having the temperature compensation circuit as described above is used, however, a reference voltage used to drive the driven device is calculated for each of the driven devices. That is, the conventional technology requires the decoupling capacitors to be connected to all of the driving circuits because temperature compensation processing needs to be processed for each of the driving circuits. Taking an LED head as an example, a conventionally used LED head 601 as shown in FIG. 26 has an LED array consisting of a combination of twenty six pieces of LED array chips as driven devices arranged on a prescribed circuit board, and also has a driving circuit IC1, IC2, . . . , IC26 arranged to correspond to the LED array chips. Furthermore, the LED head 601 has decoupling capacitors 605, 607, . . . , 657 corresponding to driving circuits IC1, IC2, . . . , IC26, respectively. The decoupling capacitors 605, 607, . . . , 657 are connected to the driving circuits IC1, IC2, . . . , IC26, respectively, arranged in proximity to the corresponding decoupling capacitors. Each of the decoupling capacitors gets rid of the noise voltage caused by the corresponding temperature compensation circuit.
In a case where the driving device as structured above is used, multiple decoupling capacitors are needed to be used, and there exists a problem that the cost of the driving device greatly increases. As shown in FIG. 26, the circuit board formed in a substantially rectangular shape has an L2 length in the short side. However, in a case where the decoupling capacitors are arranged in proximity to the driving circuits IC1, IC2, . . . , IC26, the length L2 of the short side of the circuit board is required to be more than a certain length. This causes the entire driving apparatus to become large and makes it difficult to downsize the driving device.